Normal variants: Fetal origin of posterior cerebral artery

The origin of the posterior cerebral artery, embryologically,
is from the internal carotid artery. Only later in development does the artery
attach to the apex of the basilar artery and the region between the
internal carotid and the basilar diminish in size to become the posterior
communicating

artery.
Persistence of this embryologic state occurs in approximately 15% of
people.

Case #1A

Lateral view, left carotid injection demonstrates the
origin of the left posterior cerebral artery directly from the
supraclinoid region of the internal carotid artery

.

Case #1B

AP left carotid injection in the same patient again demonstrates the
origin of the left posterior cerebral artery directly from the internal carotid artery

.

Case #2A

2D Phase Contrast MRA demonstrates origin of the left posterior
cerebral artery from the left internal carotid (arrow).

Case #2B

Lateral 3D TOF MRA from the same patient showing the posterior
cerebral artery origin from the internal carotid (arrow).